Seat mechanism



FIG. 1 is a perspective view of a seat mechanism according to my new ornamental design;

FIG. 2 is a top view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a rear view thereof;

FIG. 6 is a left side view thereof; and,

FIG. 7 is a bottom view thereof. 

The ornamental appearance of a seat mechanism, as shown. 